Methods and/or devices of the generic kind mentioned above are used in nearly all fields of electrical engineering in which digitally determined data have to be transmitted in analog form to corresponding signal receivers. An important field of application is in vehicle safety systems.
The conversion of digital values into analog signals is usually performed with digital-to-analog converters (DAC) which are in most cases available as integrated circuits. The prices of such converters rise disproportionately to the increases in conversion resolution and speed.
Another, less expensive method is the use of pulse-width modulation systems (PWM). The required PWM signals are generated from digital signals with variable pulse width and subsequently low-pass filtered. One disadvantage of this alternative method is that the resolution depends on the time base of the PWM frequency. This leads to a conflict of objectives between resolution and achievable conversion rate. Another disadvantage is that the signal level of the analog signal to be generated depends on the signal level of the PWM signals, which can make additional adaptation circuits (attenuators, amplifiers, level shifters, etc.) necessary.
Applications often require the highest possible resolution in a precisely given voltage range and at the same time a high conversion rate.
Many applications also require different voltage ranges of the analog output signals. These voltage ranges exhibit manufacturing tolerances. In addition, the voltage ranges vary due to influences of the environment, especially changes of the ambient temperature, and also depending on the lifespan of the signal converter or owing to controlled influences, i.e. intentional adjustment of operating points.
The time base for the pulse-width signal cannot be increased infinitely in most applications. If performing a conversion based on the pulse-width modulation method, the high conversion resolution at a given time base requires a longer signal time and hence a lower signal frequency of the pulse-width modulated intermediate signal. This in turn leads to a lower conversion rate and thus to a slowdown of conversion. The longer signal time also increases the complexity of the subsequent low-pass filtering of the pulse-width modulated intermediate signal, since a low cut-off frequency is required there.